Diodes AP3605 - Manual (Page 10)

10
Jan. 2013 Rev. 1. 8 BCD Semiconductor Manufacturing Limited
4-Channel Charge Pump LED Driver with Current Balancing and Wide Range PWM Dimming AP3605
Data Sheet
Operation
Figure 18. AP3605 Typical Application Circuit with 4 WLEDs
Typical Application
The AP3605 is a high efficiency 1.5x fractional
charge pump with 4 channels of integrated current
source for white LED backlight applications. The
AP3605 consists of a linear regulator followed by a
1.5x charge pump which operates at 1MHz, 4
channels current source, a reference and other control
circuits. The linear regulator regulates its output
voltage to supply charge pump, guarantees that the
charge pump always operates at 5V output with 1.5x
mode. This configuration minimizes the output
ripple.
The charge pump can generate 80mA of output
current, so each of the 4 WLED can be powered with
up to 20mA of current. The maximum LED current is
set by a resistor connected to the ISET pin which
programs a reference current, then the reference
current is mirrored to set the LED current.
Applying a PWM signal to the EN pin can be used to
achieve LED brightness dimming. Integrated 2ms
standby function helps to enhance the dimming con-
trol. Detailed descriptions please see the related
application note.
1μF
C
OUT
1 μF
C 1
C1+
EN
V
OUT1
V
IN
D1
D2
D3
GND
C
IN
1 μF
AP360 5
D 4
C1- C2- C2+
1μF C 2
I
SET
EN
R
ISET
PWM Dimming
1kHz to 50kHz
Li-ion
Battery
V
OUT2